Any idea what the "Curse of Scrambled Spells" actually does?

When my Sim had it (at the same time as the uncontrollable charge one), I ended up with fire, a duplicated litter box, and general mayhem.
I think it will only use spells that your SIm already knows so the end result does depend on that.

Basically, whatever you try to cast, there's a high chance that you'll actually cast something different. (cue the fire and duplication of things)